Segmenting a series of 2d or 3d images

ABSTRACT

The invention relates to an apparatus having means for segmenting a series of 2D or 3D images obtained by monitoring a patient&#39;s organ or other body part, wherein a first segmentation is carried out on a first image of the series of images and wherein the first segmentation is used for the subsequent segmentation of the remainder of images of said series of images. In relation to the images said means carry out a series of transformations wherein each separate transformation embodies a fitting operation between two images of said series of images, and wherein substantially all images of the series of images are subject of such a transformation. The first segmentation on the first image of the series of images is modified and subsequently applied to any further image of the series of images according to the transformation or sequence of transformations that fits the said first image to said further image of the series of images.

Method, software and apparatus for segmenting a series of 2D or 3Dimages The invention relates to a method and to an apparatus havingmeans for segmenting a series of 2D or 3D images obtained of a patient'sorgan or other body part, wherein a first segmentation is carried out ona first image of the series of images and wherein the first segmentationis used for the subsequent segmentation of the remainder of images ofsaid series of images.

Such a method and apparatus is known from U.S. Pat. No. 5,903,664,showing a cardiac segmentation system acquiring a series of images asslices through a volume, and as images at different time periodsthroughout a cardiac cycle. In this known system and method a firstimage of a series of images is segmented by making use of a threshold.The centroid of this image is used as a seed point in segmentingadjacent images. This is repeated for a number of images in order thatall images are accordingly segmented.

It is an object of the invention to improve the reliability andversatility of the known method and apparatus for segmenting a series of2D or 3D images, whereby the segmenting still can take place with littleor without human intervention.

It is also an object of the invention to provide a method and apparatus,which allow for easy and swift comparison between different sets ofimages.

These and other objects of the invention which will become apparent fromthe discussion below, are accomplished in that while in use theapparatus of the invention carries out a series of transformations inrelation to the images, wherein each separate transformation embodies afitting operation between two images of said series of images, andwherein substantially all images of the series of images are subjectedto such a transformation, whereby the first segmentation on the firstimage of the series of images is modified and subsequently applied toany further image of the series of images according to thetransformation or sequence of transformations that fits the said firstimage to said further image of the series of images.

The invention is also embodied in the method and in software operated bythe apparatus, which method and software are characterized in that inrelation to the images a series of transformations are establishedwherein each separate transformation embodies a fitting operationbetween two images of said series of images, and wherein substantiallyall images of the series of images are subjected to such atransformation, and that the first segmentation on the first image ofthe series of images is modified and subsequently applied to any furtherimage of the series of images according to the transformation orsequence of transformations that fits the said first image to saidfurther image of the series of images.

It is envisaged that any type of segmentation can be applied initiallyas the first segmentation on the first image. This segmentation can becarried out either manually or (semi) automatically by means and methodsthat are known per se in the art. The result of this segmentation whichcan be moulded according to the needs of the user, is according to theinvention simply and quickly propagated to the other images of theseries of images.

The said transformation among the respective images of the series can beapplied for instance between the said first image of the series ofimages and each of the further images of such series of images. It is,however, preferred that each transformation relates to adjacent orimmediately successive images of the series of images. The differencesbetween adjacent or immediately successive images of said series ofimages are rather limited allowing that the accuracy requirements of thetransformation remain fairly limited.

An important benefit of the invention lies in that it provesparticularly useful when there are two or more series of images, wherebythe segmentation applied to the first series of images can also beapplied to the other series of images. This allows for ease ofcomparison among the said series.

The just mentioned advantage is immediately apparent when the method isapplied to, or the apparatus operates on series of images that arecollected with different means of monitoring selected from the group MR,CT, NM and US.

It is further useful that the respective series of images, whether beingcollected with the same means of monitoring or with different means ofmonitoring, are collected at different times.

The method according to the invention applies to all types of organs andother patient's body parts. When the images, however, relate to asubstantially sphere-like organ such as a heart, the apparatus, softwareand method according to the invention are preferably characterized inthat prior to establishing the said series of transformations, theseries of images are converted to a modified series of images showingthe walls of the organ in a flat plane wherein the left and right partof said plane substantially correspond to the inside and outside of saidorgan, and that the said series of transformations are applied to themodified series of images. By this measure of converting the initialseries of images to a modified series of images, the processingaccording to the invention can be substantially alleviated allowing forrapid processing of large amounts of images without sacrificingaccuracy.

The invention shall hereafter be further elucidated with reference tothe drawing.

In the drawing:

FIG. 1 shows a schematic flow sheet of the operation of an apparatusaccording to the invention;

FIG. 2 shows schematically an image of a heart and a modified imagethereof; and

FIG. 3 shows the modified image of the heart in two subsequent images.

The invention applies to processing of both 2D and 3D images. Formedical diagnosis, therapy planning and monitoring of the effect oftherapy it is often required to accurately segment various anatomicalstructures that are present in medical images of the patient. Medicalimage segmentation has therefore received considerable attention duringthe last few decades.

Many segmentation algorithms have been proposed, ranging from methodsbased on thresholding (see U.S. Pat. No. 5,903,664) to advanced methodssuch as 2D active-contour or 3D active-object based segmentation.

Whatever the type of segmentation, which may also include manualsegmentation, the invention proposes an apparatus and method which makeit easy to apply the selected segmentation to all images in a series ofimages or to several series of images, whereby it is only required toapply an initial segmentation to a selected first image of the series ofimages.

With reference now to FIG. 1, the general working of the apparatus andmethod according to the invention is explained. An image 1 undergoes asegmentation in box 2 resulting in a desired segmented image 3. The saidfirst image 1 and consecutively further images i, whereby i may rangefrom 2 to n, are supplied to a box 4 in which a transformation T_(l,i)is calculated in order to arrive at a best fit of image 1 and image i.This transform T_(1,i) is supplied to a box 5, which also receives theinitial segmented image 3 and which converts these both informationflows into a segmented image 6 corresponding to the original image i.The apparatus of the invention repeats this process for every i in therange 2 to n, so that in relation to a region of interest of theconcerning images, a series of transformations are established, whereineach separate transformation embodies a best fit between two images ofsaid series of images, and wherein each image of the series of images issubject of such a transformation. Although FIG. 1 relates to eachindividual transformation among images such that always image 1 formspart thereof, it is also possible that each individual transformationrelates to adjacent or—in other words—immediately successive images ofthe series of images.

The invention is also applicable when there are two or more series ofimages whereby the segmentation of the first series of images (which isbased on the segmentation of the first image from this first series ofimages) applies to all series of images.

It is in this respect possible and at times advantageous that therespective series of images are collected with different means ofmonitoring the patient, which means are selected from the group MR, CT,NM and US. The respective series of images may also be collected atdifferent times.

With reference to FIG. 2, it is shown that the images (one of which isshown in the left-hand part of FIG. 2) may relate to a substantiallysphere-like organ such as a heart. In such a case, it is desirable thatprior to establishing the above explained series of transformations, aconversion of the image of the heart shown at the left-hand part takesplace to a modified image as shown in the right-hand part of FIG. 2.This type of transformation is known as a resample operation and resultsin a showing of the walls of the concerning organ in a flat plane,wherein the left- and right-hand part of said plane substantiallycorrespond to the inside and outside of the concerning organ. The easeof working of the apparatus and method of the invention is highlysupported by this prior operation allowing that the transformation cantake place to the modified image which is simpler to operate. An exampleof this is shown with reference to FIG. 3.

FIG. 3 shows at the left-hand part an image i and on the right-hand parta subsequent image i+1. The region of interest of these images is theso-called myocardium of the left ventricle of the heart, the position ofwhich is indicated in the left-hand Figure by r₁-r₂. In the right-handpart of the Figure relating to image i+1 this position has changed to r₁-r ₂. The change in position from r₁-r₂ to r ₁-r ₂ represents thetransformation that fits image i to image i+1 and which is used forapplying the segmentation of image i to image i+1.

It is remarked that the above merely represents one example of executingthe transformation as part of the method according to the invention andthat there are numerous other ways of executing this transformationwithin the scope and spirit of the invention as tined by the appendedclaims.

1. An apparatus having means for segmenting a series of 2D or 3D imagesobtained of a patient's organ or other body part, wherein a firstsegmentation is carried out on a first image of the series of images andwherein the first segmentation is used for the subsequent segmentationof the remainder of images of said series of images, characterized inthat in relation to the images said means carry out a series oftransformations wherein each separate transformation embodies a fittingoperation between two images of said series of images, and whereinsubstantially all images of the series of images are subjected to such atransformation, and wherein the first segmentation on the first image ofthe series of images is modified and subsequently applied to any furtherimage of the series of images according to the transformation orsequence of transformations that fits the said first image to saidfurther image of the series of images.
 2. An apparatus according toclaim 1, characterized in that each transformation relates to adjacentor immediately successive images of the series of images.
 3. Anapparatus according to claim 1, characterized in that there are two ormore series of images and that the segmentation of a first series ofimages is applied to all series of images.
 4. An apparatus according toclaim 3, characterized in that the respective series of images arecollected with different means of monitoring selected from the group MR,CT, NM and US.
 5. An apparatus according to claim 3, characterized inthat the respective series of images are collected at different times.6. An apparatus according to claim 1, wherein the images relate to asubstantially sphere-like organ such as a heart, characterized in thatprior to establishing the said series of transformations, the series ofimages are converted to a modified series of images showing the walls ofthe organ in a flat plane wherein the left and right part of said planesubstantially correspond to the inside and outside of said organ, andthat the said series of transformations are applied to the modifiedseries of images.
 7. Software for an apparatus arranged for segmenting aseries of 2D or 3D images obtained of a patient's organ or other bodypart, wherein a first segmentation is carried out on a first image ofthe series of images and wherein the first segmentation is used for thesubsequent segmentation of the remainder of images of said series ofimages, characterized in that in relation to the images a series oftransformations are established wherein each separate transformationembodies a fitting operation between two images of said series ofimages, and wherein substantially all images of the series of images aresubjected to such a transformation, and wherein the first segmentationon the first image of the series of images is modified and subsequentlyapplied to any further image of the series of images according to thetransformation or sequence of transformations that fits the said firstimage to said further image of the series of images.
 8. Softwareaccording to claim 7, characterized in that each transformation relatesto adjacent or immediately successive images of the series of images. 9.Software according to claim 7, characterized in that there are two ormore series of images and that the segmentation of a first series ofimages is applied to all series of images.
 10. Software according toclaim 7, wherein the images relate to a substantially sphere-like organsuch as a heart, characterized in that prior to establishing the saidseries of transformations, the series of images are converted to amodified series of images showing the walls of the organ in a flat planewherein the left and right part of said plane substantially correspondto the inside and outside of said organ, and that the said series oftransformations are applied to the modified series of images.
 11. Amethod for segmenting a series of 2D or 3D images obtained of apatient's organ or other body part, wherein a first segmentation iscarried out on a first image of the series of images and wherein thefirst segmentation is used for the subsequent segmentation of theremainder of images of said series of images, characterized in that inrelation to the images a series of transformations are establishedwherein each separate transformation embodies a fitting operationbetween two images of said series of images, and wherein substantiallyall images of the series of images are subjected to such atransformation, and that the first segmentation on the first image ofthe series of images is modified and subsequently applied to any furtherimage of the series of images according to the transformation orsequence of transformations that fits the said first image to saidfurther image of the series of images.
 12. A method according to claim11, characterized in that each transformation relates to adjacent orimmediately successive images of the series of images.
 13. A methodaccording to claim 11, characterized in that there are two or moreseries of images and that the segmentation of a first series of imagesis applied to all series of images.
 14. A method according to claim 13,characterized in that the respective series of images are collected withdifferent means of monitoring selected from the group MR, CT, NM and US.15. A method according to claim 13 or 14, characterized in that therespective series of images are collected at different times.
 16. Amethod according to claim 11, wherein the images relate to asubstantially sphere-like organ such as a heart, characterized in thatprior to establishing the said series of transformations, the series ofimages are converted to a modified series of images showing the walls ofthe organ in a flat plane wherein the left and right part of said planesubstantially correspond to the inside and outside of said organ, andthat the said series of transformations are applied to the modifiedseries of images.